1 Introduction

1.1 Background

The statutory framework for greenhouse gas ( GHG) reduction created by the Climate Change (Scotland) Act 2009 sets the ambition to reduce GHG emissions by 42% by 2020 and 80% by 2050 compared to 1990 levels (Scottish Government, 2009). As of today Scotland is on track to meet this target, with recently published data for 2014 indicating that the 2020 interim target had been met six years ahead of schedule (Scottish Government, 2016a). According to Section 35 of the Act, Scottish Ministers are under a duty to present a Report on Proposals and Policies ( RPP) to the Scottish Parliament, defining specific measures to reduce GHG emissions to meet Scotland's statutory targets. The Scottish Government published the second Report ( RPP2) in June 2013, covering the period 2013 - 2027 (Scottish Government, 2013). The Climate Change Plan sets out proposals and policies for meeting targets to 2032.

There is increasing recognition that actions designed to reduce GHG emissions not only mitigate the risks of climate change but may also either help or restrict the achievement of other societal objectives such as improved air quality, health and energy security (Committee on Climate Change, 2016). Together, these benefits and potential adverse impacts of climate change mitigation might provide additional incentives or potentially disincentives for strong actions to reduce GHG emissions or at least to heavily influence the design and implementation of emission reduction policies and measures.

A more detailed understanding of such potential co-benefits and adverse side effects is an important part of the foundation underpinning the development of future Scottish Government policies. Information on the impacts of climate change mitigation across the built environment policy area helps improve understanding of social and economic benefits and the role these could play in helping to create a fair, more equal and prosperous Scotland.

The Scottish Government commissioned Aether and Aether Associates to provide a synthesis of qualitative and quantitative evidence relevant to the Scottish context, indicating the direction and magnitude of any potential wider impacts of climate change mitigation actions in the built environment sector. Where possible the study identifies quantitative models and tools, and evaluates impacts in terms of social equality. This is the final report of the study.

1.2 Definitions and framing

Climate change mitigation action is typically evaluated in terms of the GHG emissions avoided per unit of expenditure, often expressed as cost per tonnes of CO 2 equivalent. The GHG savings will lead to benefits arising from reduced climate change, such as lower sea level rise and fewer extreme weather events. However, these actions usually have other impacts - both positive and negative - beyond the benefits of avoided climate change and the direct financial costs of the mitigation action. These wider impacts are referred to as co-benefits if they are positive and adverse side-effects if they are negative, sometimes jointly referred to as co-impacts. In the built environment sector, for example, increased levels of insulation and draught-proofing could give rise to a range of co-benefits including the health and wellbeing benefits from more comfortable living conditions (Smith et al., 2015). However, an increase in concentrations of air pollutants if ventilation is reduced could subsequently lead to adverse health impacts (Citizens Advice Scotland, 2016; Wilkinson et al. 2009). It is often possible to mitigate adverse side-effects, in this example through installing additional ventilation options ( e.g. Vardoulakis et al., 2015).

When considering the financial costs of energy consumption, it can be hard to define the boundary between direct costs and benefits and co-impacts. For example, energy efficiency in buildings should lead to reduced energy costs. These energy cost savings are widely treated as a co-benefit in the literature, but they are also often included in the cost-benefit assessments that contribute to the GHG mitigation investment decision - in other words, they are included in the calculation of the cost per tonne of CO 2 avoided. It is important to avoid double-counting these benefits. Conversely, the literature does not generally treat any increases in household energy prices arising from investment in low carbon energy generation as an adverse side-effect, as these are generally assumed to be factored into climate policy assessments. In both cases, however, changes in energy costs can be treated as co-impacts if they have unintended side-effects, e.g. if they fall disproportionately on particular sectors of society - either increasing or decreasing fuel poverty and social inequality.

Although most co-benefit studies refer to the wider impacts of climate change mitigation policies, as described above, some address the impacts of non-climate policies, such as air quality legislation, on greenhouse gas emissions. For example, the use of biomass stoves in built-up areas can be restricted to protect urban air quality, and this could limit the potential for low-carbon heating in buildings [1]. There are also studies that take a more holistic view, assessing all the impacts of a technology or policy on an equal basis, including both climate and non-climate impacts. Although some early studies defined co-benefits as 'benefits not related to the primary aim of a policy or action', it is now acknowledged that not all policies or actions have a single primary aim, and it could be better to assess all impacts within a 'multiple objective, multiple impact' framework (Ürge-Vorsatz et al., 2014). A number of papers now refer to 'multiple benefits', including GHG savings alongside other impacts, rather than co-benefits. All these different framings are addressed in this report.

This report focuses on the wider impacts of GHG reduction measures. These wider impacts need to be considered alongside the cost-effectiveness and abatement potential of each mitigation option for greenhouse gas reduction, so that policies can be designed to meet climate targets while maximising co-benefits and reducing adverse side-effects.

1.3 Research aim and objectives

The aim of this project is to increase the Scottish Government's understanding of the potential wider impacts for Scotland of climate change mitigation actions to support the development of the Climate Change Plan.

The objectives of this project are:

To produce a synthesis of qualitative evidence which indicates the direction (positive/ negative) and potential magnitude of the potential wider impacts of climate change mitigation actions which would be relevant to the Scottish context.

To identify the most robust quantitative models and tools which would enable quantification and, where possible, monetisation of the potential wider impacts of climate change mitigation actions which would be relevant to the Scottish context.

These objectives are underpinned by the following research questions:

1) What is the evidence, both quantitative and qualitative, of potential wider impacts (co-benefits and adverse side effects) arising from climate change mitigation actions which would be relevant to the Scottish context?

2) Based on a review and synthesis of qualitative evidence: what are the key sources of robust evidence; and what is the balance of evidence, in terms of direction (positive/negative) and potential magnitude, of those wider impacts relevant to Scotland?

3) Based on a review and synthesis of quantitative evidence: which models and tools are assessed as the most robust to quantify and, where possible, monetise such wider impacts? What quantitative data would be required to apply these models to Scotland? What key assumptions are required?

4) From an equalities perspective, what evidence is there about the potential distribution of wider impacts relevant to Scotland across the population?

5) What are the most significant gaps in research and evidence about potential wider impacts which are relevant to Scotland?